1. Field of the Invention
This invention relates to the field of integrated circuit (IC) fabrication, and particularly to the fabrication of capacitors and thin film resistors on a common substrate.
2. Description of the Related Art
The ability to integrate high accuracy passive components such as resistors and capacitors with active devices has become increasingly important. Capacitors having a poly-oxide-poly structure have traditionally been employed in this context, because they are simple and inexpensive to fabricate. Unfortunately, the capacitance value of such devices varies significantly with applied voltage, and their inherently high resistance and parasitic capacitance components make them unsuitable for many high performance analog circuits.
A capacitor having a metal-oxide-metal structure avoids these deficiencies, and can in general be placed further from the supporting substrate, thereby lowering the parasitic capacitive components. For manufacturing efficiency, one level of interconnect metal is typically incorporated as either the top or bottom plate of the capacitor. However, this technique can lower the effectiveness of the capacitor, due to limitations imposed on the metal etch used for the top and/or bottom plates.
Similar problems are encountered when integrating resistors. Polysilicon resistors are simple and inexpensive to fabricate, but their resistance values vary with applied voltage and temperature, they exhibit high parasitic capacitance, and often have poor matching characteristics. Thin film resistors formed from metal or metal combinations have been formed to overcome these shortcomings. Such resistors are generally integrated with one of the metal interconnect levels to improve manufacturing efficiency. Unfortunately, this can lead to degradation in the resistors"" matching characteristics due to the metal thickness dictated by the interconnect level, or due to the irreproducibility of the dimensions of each resistor""s active opening in the metal when it is cleared to expose the resistor.
An IC resistor and capacitor fabrication method is presented which overcomes the problems noted above, providing high performance thin film resistors and metal-dielectric-metal capacitors on a common substrate.
In accordance with one embodiment of the present method, an IC""s active devices and a metal interconnect level are fabricated on a substrate. A dielectric layer is deposited over these structures, which protects them from the subsequent process steps required to form the resistors and capacitors. A layer of thin film material suitable for the formation of thin film resistors (TFRs) is deposited next, followed by a metal layer that will form the bottom plates of the metal-dielectric-metal capacitors. Next, the capacitors"" dielectric layer is deposited to a desired thickness to target a particular capacitance value, followed by the deposition of another metal layer that will form the capacitors"" top plates. The metal layers, the capacitor dielectric layer, and the thin film material layer are patterned and etched to form TFRs and metal-dielectric-metal capacitors as desired on the IC substrate.
The method may be practiced using any of several alternative process sequences. For example, the bodies of the TFRs can be formed before the deposition of the capacitors"" layers. Also, the capacitors"" bottom plates may be patterned and etched prior to doing the same for their top plates.
Further features and advantages of the invention will be apparent to those skilled in the art from the following detailed description, taken together with the accompanying drawings.